1. Field of the Invention
The present invention relates to a technology for controlling an output of an output device by a feedback control.
2. Description of the Related Art
To maintain a constant electric power that is output from a power supply device or a motor driving device, the electric power is controlled based on feedback data that is obtained by calculating a duty cycle of, for example, a pulse-width modulation (PWM) signal, and then calculating a difference between the calculated duty cycle and a reference duty cycle.
As a technology to implement an appropriate feedback control, for example, Japanese Patent Application Laid-open No. H7-203672 discloses a PWM control in which a first case where a voltage output from the electric power of the power supply device is larger than a target value is differentiated from a second case where the voltage is smaller than the target value to maintain the constant electric power output from the power supply device.
However, in the PWM control disclosed in Japanese Patent Application Laid-open No. H7-203672, the same correction amount is used in both the first case and the second case. Therefore, as it is clear from the examples shown in FIGS. 8A and 8B with the target value of 50, different initial values of the PWM signals before the feedback control (41 in the example shown in FIG. 8A, and 49 in the example shown in FIG. 8B) disadvantageously result in different averages of the PWM signals after the feedback control. In other words, the output of the electric power changes depending on the initial value of the PWM signal.